1. Technical Field
The present disclosure relates to a power semiconductor device, in particular, to a trench power semiconductor device having shielding electrode.
2. Description of Related Art
Please refer to FIG. 1, which shows a cross-sectional schematic view of a prior art trench power transistor. The trench power transistor 1 includes two gates 130a, 130b and a shielding electrode 140, which are arranged in the same trench 100h and parallel to one another. The two gates 130a, 130b, and the shielding electrode 140 are insulated from one another through an oxide layer 131. During the fabrication of the trench power transistor 1, a portion of the shielding electrode 140 and a portion of the sidewalls of the trench 100 are oxidized by performing a thermal oxidation process to form the oxide layer 131 for isolating the shielding electrode 140 form the two gates 130a, 130b and a gate oxide 132. However, too thin a thickness of the oxide layer 131 fabricated by the thermal oxidation process results in higher capacitances between each of the gates 130a, 130b and the shielding electrode 140.
Furthermore, subjected to the limitation of the process conditions, the bottom portion of the oxide layer 131 is hard to form and is relatively thin. As such, each of gates 130a, 130b has a point portion 130s located at the bottom side closer to the shielding electrode 140. Therefore, the point effect easily occurs, thereby reducing the withstand voltage of the gates 130a, 130b and inducing the degradation of the gate under high temperature. Accordingly, the reliability of the power metal oxide semiconductor field transistor would decrease thereby affecting the lifetime of the trench power transistor.